The present invention is related to an improved aeration device, more specifically to an accessory-equipment to be used in protecting all kinds of aeration devices designed for oxygenating the water in aeration-sedimentation basins, such as biological aeration basins, digestion basins or particularly aerated facultative lagoons. In order to simplify the wording of the following description, only the word "basins" will be used hereinafter to identify both the basins and lagoons.
In fact, the present invention can be readily applied to all aeration devices called "static aerators" used for oxygenating the water in a basin of the above type. In such a basin, industrial or municipal sewage and waste water are treated by subjecting them to an aerobic digestion. To achieve this aerobic digestion, oxygen is injected in the water of the basin. Although it can be used in all applications, the invention is particularly suitable for use in aerated facultative basins where large solid accumulations are permitted for long time periods.
The presence of solid accumulations constitutes a real threat to any air diffusing system using static aerators as it will eventually
cause a serious clogging problem;
decrease aeration performance.
These inconveniences are presently being somewhat overcome by costly operation and maintenance means. Even with these means, no intermittent operation of the aerators is recommendable as clogging possibilities will increase in proportion with the "stop-start" operation and with the importance of the solid accumulations at the bottom of the basin. Also, circulation of anaerobic solids through the aerator represents a waste of energy as considerable oxygenation capacity of the installed equipment is being used to oxygenate solids that in a facultative process (water being treated aerobically and solids anaerobically) are meant to be treated anaerobically at the bottom of the basin.
The evolution of the clogging problem will depend upon the rate of accumulation of solids (sludge), and will also depend on the number of times and the frequency at which the aerator operation will be interrupted for any given reason (maintenance, power failure, noise inconvenience, energy conservation, etc . . . ).
Conventionally, a static aerator is immersed and formed with an aeration column provided with a lower inlet and with an upper outlet. Air under pressure is supplied through an air line provided with an orifice to produce in the column an upward jet of air. The air jet causes flowing of water through the column from its inlet to its outlet while oxygenating the water.
Each time the supply of pressurized air to a static aerator is interrupted, some water enters the air line through the calibrated air outlet orifice which is drilled on this pressurized air feeding line. Since this orifice is always located close to the bottom of the basin where sludge accumulates, water entering in the air line will carry an important quantity of solids.
When the supply of pressurized air is restored, most of the solids are exhausted with the water through the orifice. However, a small quantity of solids remains inside the air line and sticks to the internal wall of the pipe. Shortly after, warm air dries off and cooks these deposits on the wall surface.
After a certain number of repetitions, a large amount of solid deposits are formed within the air line. These deposits will eventually detach from the internal surface of the air pipe and be blown out through the orifice. The larger deposits will, along with any relatively large solids, clog the orifices partially or completely. Some of these solids will build up and become very hard if a certain chemical reaction occurs.
Other types of blockage are also observed with larger solids (organic and inorganic) and with fibrous/hairy material that can attach easily to every sharp edge. These types of material are normally found in all municipal sewage and have a tendency to cause clogging right at the lower water inlet of the aeration column and/or at the air exhaust orifice that is drilled on the air supply pipe inside each aerator.